Handheld thermal imaging cameras, for example, including microbolometer detectors to generate infrared images, are used in a variety of applications, which include the inspection of buildings and industrial equipment. Many state-of-the-art thermal imaging cameras have a relatively large amount of built-in functionality allowing a user to select a display from among a host of display options, so that the user may maximize his ‘real time’, or on site, comprehension of the thermal information collected by the camera.
As is known, infrared cameras generally employ a lens assembly working with a corresponding infrared focal plane array (FPA) to provide an image of a view in a particular axis. The operation of such cameras is generally as follows. Infrared energy is accepted via infrared optics, including the lens assembly, and directed onto the FPA of microbolometer infrared detector elements or pixels. Each pixel responds to the heat energy received by changing its resistance value. An infrared (or thermal) image can be formed by measuring the pixels' resistances—via applying a voltage to the pixels and measuring the resulting currents or applying current to the pixels and measuring the resulting voltages. A frame of image data may, for example, be generated by scanning all the rows and columns of the FPA. A dynamic thermal image (i.e., a video representation) can be generated by repeatedly scanning the FPA to form successive frames of data. Successive frames of thermal image data are generated by repeatedly scanning the rows of the FPA; such frames are produced at a rate sufficient to generate a video representation of the thermal image data.
Also as is known, the lens assembly often includes a stationary lens body mounted to a camera housing. The lens body supports a rotatable focus ring for focusing the lens. Rotation of ring within the lens body results in axial movement of the ring and the lens relative to the lens body, which remains stationary, due to the cam action of the lens body. Lens position sensors may be employed to determine the lens focus position. However, in some lens assembly designs, the focus changes from its minimum distance to its maximum distance over a very short axial translation. The short axial translation does not provide much axial translation over which lens position sensors may be used to measure the focus position. Accordingly, the resolution and therefore the accuracy of the lens position sensors in such instances may be compromised.